In the early Middle Ages investigation of heresy was a duty of the bishops. Alarmed especially by the spread of Albigensianism (see Albigenses), the popes issued increasingly stringent instructions as to the methods for dealing with heretics. Finally, in 1233, Pope Gregory IX established the papal Inquisition, dispatching Dominican friars to S France to conduct inquests.
When an inquisitor arrived, a month of grace was allowed to all who wished to confess to heresy and to recant; these were given a light penance, which was intended to confirm their faith. After the period of grace, persons accused of heresy who had not abjured were brought to trial. The defendants were not given the names of their accusers, but they could name their enemies and thus nullify any testimony by these persons. After 1254 the accused had no right to counsel, but those found guilty could appeal to the pope. The trials were conducted secretly in the presence of a representative of the bishop and of a stipulated number of local laymen. Torture of the accused and his witnesses soon became customary and notorious, despite the long-standing papal condemnation of torture (e.g., by Nicholas I); Innocent IV ultimately permitted torture in cases of heresy.
Most trials resulted in a guilty verdict, and the church handed the condemned over to the secular authorities for punishment. Burning at the stake was thought to be the fitting punishment for unrecanted heresy, probably through analogy with the Roman law on treason. However, the burning of heretics was not common in the Middle Ages; the usual punishments were penance, fine, and imprisonment. A verdict of guilty also meant the confiscation of property by the civil ruler, who might turn over part of it to the church. This practice led to graft, blackmail, and simony and also created suspicion of some of the inquests. Generally the inquisitors were eager to receive abjurations of heresy and to avoid trials. Secular rulers came to use the persecution of heresy as a weapon of state, as in the case of the suppression of the Knights Templars.
The Inquisition was an emergency device and was employed mainly in S France, N Italy, and Germany. In 1542, Paul III assigned the medieval Inquisition to the Congregation of the Inquisition, or Holy Office. This institution, which became known as the Roman Inquisition, was intended to combat Protestantism, but it is perhaps best known historically for its condemnation of Galileo. After the Second Vatican Conference, it was replaced (1965) by the Congregation for the Doctrine of the Faith, which governs vigilance in matters of faith.